AU669467B2

AU669467B2 - Hot press

Info

Publication number: AU669467B2
Application number: AU17668/95A
Authority: AU
Inventors: Mitsumasa Horikawa; Yasuo Tamura
Original assignee: Koyo Sangyo Co Ltd
Current assignee: Koyo Sangyo Co Ltd
Priority date: 1994-05-06
Filing date: 1995-04-28
Publication date: 1996-06-06
Anticipated expiration: 2015-04-28
Also published as: AU1766895A; CN1117911A; JP2742212B2; CN1094413C; JPH07299810A

Description

I

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: Koyo Sangyo Co., Ltd.

Actual Inventor(s): Mitsumasa Horikawa Yasuo Tamura Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: HOT PRESS Our Ref 409492 POF Code: 65131/65149 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1- HOT PRESS Background of the Invention [Field of the Invention] The present invention relates to a hot press suited to hot-press a workpiece made of a sheet of plywood, a sheet of laminated veneer lumber (LVL), a particle board, a flake board, a fiber board, a hard board, and a sheet-like object which are made of lignocellulose while injecting steam or gas.

More particularly, the present invention relates to a hot press provided with a spacer having a plurality of injection holes for injecting pressured and heated steam or gas between heating plates.

In this specification, a "workpiece" represents a laminate to be pressed and a "product" represents a pressed laminate.

[Description of the Prior Art] A product such as a sheet of plywood, a particle board, or a fiber borrd, each of which is made of lignocellulose, has hitherto been formed into a place by applying an adhesive to the surface of a plurality of veneers, sheets of wood (chips), or fibers and thereafter superimposing them, arranging the superimposed workpiece between a pair of heated pressing plates of a hot press, and hot-pressing the workpiece. In this case, a predetermined hot-pressing time is required to .i heat and harden the adhesive. In particular, to manufacture a thick product, it is necessary to hot-press a workpiece for a long time by considering the time when heat is transmitted up 1ito the inside of the workpiece. The hot-pressing time directly relates to the production time. Therefore, the longtime hot-pressing is an obstacle for mass production and moreover raises the unit price of a product.

To solve the above problem and decrease the hot-pressing time, the steam injection pressing method has been used so far. This pressing method, as shown in Fig. 11, comprising forming a lot of small injection holes 2a on the pressing surfaces of a top heating plate 1 and a bottom heating plate 2 of a press and injecting pressured and heated steam or gas from the injection holes 2a. In the case of this method, steam pipes 3 arranged on the heating plates 1 and 2 are connected to the small injection holes 2a on each pressing surface and provided with an on-off valve 3a comprising a solenoid valve respectively. Heated and pressured steam or gas sent from the steam pipes 3 is injected from the small injection holes 2a and a workpiece 4 is heated by the steam or the like. hereby, the whole workpiece instantaneously reaches the hardening temperature of an adhesive. Therefore, the time is greatly decreased and the productivity can be improved.

Examples of the steam injection press are disclosed in a "method of pressing a particle board by a press" provided with a chamber demarcating apparatus for demarcating a chamber enclosing an area between a pair of pressing plates (Ckamined Published Japanese Patent Application No. 57-1416) a "steam injection press" provided with a nozzle heater for heating a steam injection nozzle up to a temperature exceeding the steam condensation temperature (Unexamined Published Japanese Patent Application No. 2-192906), and a "gas injection press for hot-pressing an intermediate product of a long plate-like object" provided with a cold pressing board adjacently to a plate for injecting steam (Unexamined Published Japanese Patent Application No.

4-113809) The "method of pressing a particle board by a press" (Examined Published Japanese Patent Application No. 57-1416) quickly hardens an adhesive by injecting steam from injection holes formed on a pressing plate in a chamber demarcating apparatus and thereby quickly transmitting heat. Moreover, the "steam injection press" (Unexamined Published Japanese Patent Application No. 2-192906) improves the productivity by preventing drops of water from being produced in a steam injection nozzle by a nozzle heater. Furthermore, the "gas injection press for hot-pressing an intermediate product of a long plate-like object" (Unexamined Published Japanese Patent Application No. 4-113809) prevents a workpiece from becoming a half-hardened state before it is hot-pressed and hardened by a cooling plate in order to continuously hot-press and harden workpieces.

However, none of the apparatuses disclosed in the above Publications use the heating plate for pressing of an existing 23 hot press because it is necessary to form injection holes for injecting steam or the like on top and bottom pressing surfaces and steam pipes connected with these injection holes S are set to another pressing surface.

,:Wi? a e• Therefore, the cost for manufacturing the heating plate for pressing increases and thus, a press is necessarily made expensive. Moreover, to newly hot-press a workpiece greatly different from the whole injection area of steam or the like formed by a lot of injection holes, it is necessary to prepare another heating plate for pressing whose number of injection holes and position are changed correspondingly to the area of the workpiece.

Furthermore, because steam injecting holes are formed on a pressing surface, there is a problem that the surface of a workaiece is deteriorated due to moisture and is not smoothed because creases and waves are produced on the surface when superimposing materials such as paper and fiber boards inferior in water resistance on the surface of the workpiece.

Furthermore, there is a problem that stains attach to the surface of workpiece because a plate-like object clogs injection holes and injection of steam or the like is prevented or unnecessary steam drain drops onto the plate-like object from the injection holes when the flat plate-like S object inferior in air permeability is superimposed on the surface of the workpiece for reinforcement or decoration.

Summary of the Invention It is an object of the present invention to provide an improved hot press.

According to the invention there is provided a hot press including a top heating plate, a bottom heating plate, and a spacer set to either or both of the pressing surfaces of the top heating plate and the bottom heating plate to determine a machining thickness of a workpiece to be pressed by the both heating plates; wherein the inner surface of the spacer facing the pressed workpiece are provided with a plurality of injection holes for injecting pressured and heated steam or gas.

The structure of the present invention for achieving the above objects is described below by referring to Fig. 1 corresponding to an embodiment.

The hot press 10 of the present invention comprises a top heating plate 11, a bottom heating plate 12, and a spacer 14 set to either or both of the pressing surfaces of the top heating plate 11 and the bottom heating plate 12 to determine a machining thickness of a workpiece to be pressed by the both heating plates 11 and 12.

The structure of the hot press of the present invention is characterized in that the inner surface 14a of the spacer 14 facing the pressed workpiece 13 are provided with a plurality of injection holes 14b for injecting pressured and heated steam or gas.

It is also possible to constitute the hot press 10 of the S o e al present invention by forming a threaded hole on the heating plate 11 or 12 of an existing hot press and securing the spacer 14 to the plate with a screw.

By setting the workpiece 13 in the spacer 14, pressing the workpiece 13 by the pair of heating plates 11 and 12, and simultaneously injecting pressured and heated steam from a plurality of injection holes 14b formed on the spacer, the injected steam permeates the workpiece 13, transmits energy, and instantaneously heats the whole workpiece 13 up to a predetermined temperature. By using the spacer 14 as an enclosing body for enclosing the workpiece 13, the workpiece 13 is hermetically sealed by the spacer 14 together with the top heating plate 11 and the bottom heating plate 12 and injected steam efficiently permeates the workpiece.

As shown in Figs. 9 and 10, even by superimposing a material inferior in water resistance or a plate-like object 32 inferior in air permeability on the both surfaces of the workpiece 13, steam can be permeated into the workpiece and moreover, the surface of the pressed workpiece 13 is kept smooth and free from stains.

Brief Description of the Drawinrs Fig. 1 is a perspective view of the hot press of an embodiment of the present invention for hot-pressing a workpiece comprising only a plurality of sheet-like objects; Fig. 2 is a top view of the bottom heating plate of the hot press in Fig. 1; Fig. 3 is a sectional view of the hot press of an 6 embodiment for hot-pressing a workpiece obtained by superimposing a plate-like object on the both sides of a plurality of sheet-like objects; Fig. 4 is a sectional view of the hot press of another embodiment for hot-pressing a workpiece obtained by superimposing a metallic plate on the both sides of a plurality of sheet-like objects; Fig. 5 is a perspective view of a plant stalk serving as an originating material of a workpiece; Fig. 6 is a perspective view of a compression roller for causing a crack on a skin of the plant stalk in Fig. 5 by compressing the plant stalk; Fig. 7 is a side view of a workpiece obtained by superimposing a plurality of sheet-like objects so that all plant stalks of the sheet-like objects orient toward the same direction; Fig. 8 is a side view of a workpiece obtained by superimposrng a plurality of sheet-like objects so that the arrangement direction of the plant stalks of some of the sheet-like objects differs from that of the plant stalks of other sheet-like objects; Fig. 9 is a perspective view showing a state in which a plurality of sheet-like objects are superimposed so that the arrangement direction of the plant stalks intersects each other, and then a plate-like object is superimposed on the both sides of the superimposed objects; Fig. 10 is a side view of a workpiece obtained by superimposing a plate-like object on the both sides of the superimposed sheet-like objects; and Fig. 11 is an illustration corresponding to Fig. 1 showing an existing hot press.

7 Description of the Preferred Embodiments Embodiments of the present invention are described below in detail by referring to the accompanying drawings.

As shown in Fig. 1, the hot press 10 has the top heating plate 11 at its top and the bottom heating plate 12 at its bottom. As for this embodiment, the bottom heating plate 12 is secured and the top heating plate 11 vertically moves so as to press the workpiece set between the plates 11 and 12. The bottom heating plate 12 is provided with the spacer 14. The spacer 14 determines the thickness of the hot-pressed workpiece 13. In the case of this embodiment, the q.uadrangular workpiece 13 is formed into a quadrangular-framelike enclosing body for enclosing the workpiece 13 correspondingly to the shape of the workpiece 13. Threaded holes (not illustrated) are formed at predetermined positions of the bottom heating plate 12 and the quadrangular-frame-like spacer 14 is secured there by six screws 15. The spacer 14 is constitute'dTso as to hermetically seal the workpiece 13 together with the top hating plate 11 and the bottom heating plate 12 under a pressured state.

A plurality of injection holes 14b for injecting pressured and heated steam or gas are formed in a line on the inner surface 14a of the spacer 14 facing the pressed workpiece 13, Thereby, it is possible to efficiently make the steam or the like injected from the injection holes 14b permeate up to the inside of the workpiece 13. It is preferable for the spacer 14 to have a thickness of at least 8 mm. This is because hot-pressing can be performed by only top and bottom heating plates for a relatively short time to obtain a workpiece with a thickness of less than 15 mm by hotpressing the workpiece by the spacer 14 with a thickness of less than 15 mm and moreover, the hot-pressing-time decreasing effect increases when the spacer 14 has a thickness of 15 mm or more.

As shown in Fig. 2 in detail, a lot of injection holes 14b are formed on 4 inner surfaces 14a of the spacer 14 respectively at equal intervals in parallel with the pressing surface of the bottom heating plate 12. The injection holes 14b are connected each other inside the spacer 14 as shown by a broken line and connected to a steam pipe 16 set on the outer surface of the spacer 14. The steam pipe 16 is provided with an on-off valve 17 comprising a solenoid valve.

As shown in Fig, 3, steam pipes lla and llb for heating the heating plates 11 and 12 are arranged zigzag in the heating plates 11 and 12 though not illustrated. Moreover, the steam pipes lla and 12a are provided with entrance and exit valves comprising a solenoid valve respectively though not illustrated so that the temperature of the heating plates 11 and 12 can be controlled by introducing or cutting off the steam heated by the steam pipes lla and 12a by the solenoid valve, A laminate made by superimposing one or more objects selected froi the group consisting of a sheet: of plywood, a heiet of laminated veneer lumber, a particle board, a Elake board, a 9 fiber board, a hard board, and a sheet-like objet which are made of lignocellulose is listed as the workpiece 13 to be machined by the hot press 10 of this embodiment. A -;:et-like molded object made of a plurality of linear stalks of an annual plant such as bagasse, cotton, bamboo, sunflower, koaliang, corn, sorghum, or sugar cane is listed as the sheet-like object made of lignocellulose. It is possible to form the sheet-like object by not only using one type of an annual plant but also combining two types of annual plants or more.

As shown in Fig. 5, the workpiece 13 of this embodiment to be pressed is made by directly compressing a plant stalk of a structure having an epidermis 20a mainly made of lignocellulose and a porous medulla 20b at its core by compression rollers 21 and 22 without cutting open the stalk 20 to cause a crack 23 on the epidermis as shown in Fig. 6, thereafter soaking the plant stalk 20 in a curing solution such as a phenolic solution to impregnate-the stalk 20 with a predetermined amount of the curing solution, moreover forming a lot of compressed plant stalks 20 into a sheet-like object 30 by netting them like a reed screen with a string 24 as shown in Fig. 1, and superimposing a plurality of sheet-like objects 30 each other while applying an adhesive to each of the sheet-like objects To form a laminate by using only sheet-like objects, it is necessary to give floxural strength uniform in all directions to the objects. To prevent the lamninat-e from warping, the workpiece 13 is formed by superimposing a 10 plurality of sheet-like objects 30 so that the plant stalks constituting the laminate intersect every sheet-like object as shown in Fig. 1. To extremely increase the bending strength in a specific direction, the workpiece 13 is formed by superimposing a plurality of sheet-like objects 30 so that the component plant talks 20 orient toward the same direction as shown in Fig. 7. It is also possible to form the workpiece 13 by making the plant stalks constituting some sheet-like objects 30 intersect with the plant stalks constituting other sheet-like objects 30 as shown in Fig. 8.

A workpiece can be formed by only plant stalks. However, as shown in Fig. 9 and Fig. 10, it is also possible to form the workpiece 13 by combining the sheet-like objects 30 made of plant stalks with the platelike objects 32. The plate-like object 32 uses a woody plate-like material such as a wood veneer, a sawed timber, a sheet of laminated wood, a sheet of plywood, a particle board, a hard board, an insulation board, a fire board, a sheet of laminated veneer lumber, a lumbered plate, or a corrugated board; a metallic plate such as an iron plate, a galvanized sheet iron, a painted steel plate, a stainless steel plate, an aluminum plate, a copper plate, or a lead plate; an inorganic platelike material such as a calcium silicate plate, a wood wool cemented board, an asbestos cement plate, or a gypsum board; or a synthetic-resin plate-like material such as a sheet of polyvinyl chloride resin, a sheet of acrylic resin, a sheet of styrol resin, a sheet of ABS resin, a sheet of AS rosin, a sheet of phenol resin, a sheet of melamine resin, a shoet of 11 urea resin, a sheet of polyethylene, or a sheet of polypropylene.

For a plate-like object, it is also possible to use a plate having an irregular surface such as a corrugated plate or a keystone plate, an expanded plate, or a reticular plate.

As shown in Fig. 4, it is also possible to set the spacer on the pressing surface of the top heating plate 43 of the hot press 40. In this case, the workpiece 42 can easily be mounted on the bottom heating plate 44. In Fig. 4, symbols 43b, 43d, and 44d represent steam pipes, 43c represents an onoff valve, and 45a represents an injection hole. Moreover, symbol 41 represents a metallic plate for smoothing the surface of the pressed workpiece 42.

The workpiece 13 comprising a plurality of sheet-like objects 30, the workpiece 13 comprising a plurality of sheetlike objects 30 and a plurality of plate-like objects 32, or the workpiece 42 comprising a plurality of sheet-like objects and a plurality of metallic plates 41 is temporarily pressed and then integrally hot-pressed by the hot press 10 or The hot press 10 shown in Figs. 1 to 3 is described below. The heating plates 11 and 12 are heated by the heated steam introduced into the steam pipes lla and 12a provided on the heating plates 11 and 12 respectively. It is preferable that the temperature of the steam injected from the injection hole 14b formed on the spacer 14 ranges between 50 and 250°C and the pressure of the steam ranges between 2 and 30 kg/cm 2 12 -L I In this case, it is preferable to set the temperature of the heating plates 11 and 12 to a value higher than the temperature of the steam injected from the injection hole 14b.

After the heating plates 11 and 12 reaches a predetermined temperature, the workpiece 13 set to the inside partitioned by the spacer 14. The top heating plate 11 is lowered to press the workpiece 13. Then, steam is injected from the injection hole 14b to heat the workpiece 13. In this case, the steam is injected from the injection hole 14b when the workpiece 13 is hermetically sealed by the heating plates 11 and 12 and the spacer 14 or when the heating plates 11 and 12 press the workpiece 13 and their pressure reaches a -redetermined value. The injection time is selected in the range of several seconds to several minutes in accordance with the thickness of the workpiece and presence or absence of a plate-like object. Under the pressured state, the on-cff valve 17 serving as a solenoid valve set to the steam pipe 16 is opened a-d pressured and heated steam is injected from the injection holes 14b formed on the spacer 14. The injected o steam permeates the workpiece 13 similarly to the case of the existing steam injection pressing method to transmit thermal energy and instantaneously heats the whole workpiece 13 up to a predetermined temperature, After the above heating and pressuring state is kept for a predetermined time, the on-off valve 17 is closed to stop the injection of the steam from the injection holes 14b and the top heating plate I. is raised to complete a series of heating and pressuriag pcocesses, 13 III II To inject pressured and heated steam or gas into a workpiece being hot-pressed, if the workpiece is strongly compressed, the workpiece is densified, the void in the workpiece decreases, and permeation of the steam or gas into the workpiece greatly decreases. Most normal products have a thickness of 15 mm or less. However, to manufacture a product with a thickness of 15 mm or more, a method of first manufacturing a product such as a thin laminate and then superimposing a plurality of the thin laminates each other is used. The hot press of this embodiment makes it possible to laminate a product with a thickness of 15 mm or more through one-time hot-pressing and thereby greatly improve the production efficiency. To manufacture a product such as a laminate with a thickness of 200 mm or more, however, it is difficult to perform hot-pressing unless the stroke interval of the hot press is increased, the volume of the hot press inevitably increases, and the equipment cost also increases.

Therefore, it is preferable that a product such as a laminate has a thickness of 15 to 200 mm.

Then, an embodiment is described below which uses the hot press in Fig. 4 whose top heating plate is provided with a spacer.

<Embodiment 1> Chips obtained by crushing pieces of a plywood veneer by a chipper are dried up to a moisture content of 4% or less. A glue solution is prepared by mixing 100% weight part of concentration urea resin adhesive of the low formaldehyde type 14 IL s-_ made in a laboratory on trial, two weight parts of 25% aqueous ammonia, five weight parts of paraffin emulsion ("CER-45" made by MOBIRU SEKIYU KABUSHIKI KAISHA) and one weight part of ammonium chloride powder. The dried chips are coated with the glue solution by a spray so that the solid content of the adhesive comes to 10% to the dried chips and then set in a wood frame and compressed to preliminarily mold it.

A quadrangular-frame-shaped aluminum spacer with a thickness of 40 mm is set to the top heating plate of the hot press. Injection holes are formed in a line on the inner surface of the spacer as shown in Fig. 2. The top heating plate is a fixed plate and kept at 150 0 C by a steam pipe set in the spacer. The vertically-moving bottom heating plate is similarly constituted and kept at 150°C, A preliminarilyshaped chip molded object slightly smaller than the spacer frame is mounted on the bottom heating plate, the bottom heating plate is raised, and the chip molded object is first hot-presse'd-ty the top and bottom heating plates at a pressure of 20 kg/cm 2 Immediately after the bottom heating plate contacts the spacer, the steam at a temperature of 150°C and a pressure of 5 kg/cm 2 is injected from the spacer for 1 min.

After one minute passes, the molding pressure is decreased to kg/cm 2 and compression is further continued for 3 min.

Thereafter, the workpiece is taken out of the hot press and left as it is for approx. one week at the room temperature to obtain a particle board with a thickness of 40 mm.

<Comparative example 1> 15 I I A hot press is used which is the same as the embodiment 1 except to set two square-pole-shaped spacers with a thickness of 40 mm free from injection holes to a top heating plate along the both sides of a workpiece. Top and bottom heating plates are kept at 150 0 C respectively to hot-press a chip molded object at a pressure of 20 kg/cm 2 for the first 5 min and thereafter hot-press it at a pressure of 10 kg/cm 2 for min. Then, a particle board with a thickness of 40 mm is obtained similarly to the case of the embodiment 1.

On the particle boards of the embodiment 1 and the comparative example 1 thus obtained, the bending strength, peeling strength, and thickness increase rate are measured in accordance with the U-type test method specified in JIS A 5908. Table 1 shows the test results.

[Table 11 Specific Bending Peeling Thickness gravity strength strength increase rate Embodiment 1 0.62 130 kgf/cm 2 2,2 kgf/cm 2 9 Comparative 0,62 136 kgf/cm 2 1.8 kgf/cm 2 18 example 1 From Table 1, it is found that the particle board of the comparative example 1 has a bending strength slightly larger than that of the particle board of the embodiment 1 but the particle board of the comparative example 1 has a lower peeling strength and a larger thickness increase rate than the particle board of the embodiment 1. This is probably because the particle board of the embodiment 1 is uniformly hardened 16

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up to its inside but the both sides of the particle board of the comparative example 1 is slightly hardened compared to the board inside.

<Embodiment 2> Woody fiber fibrillated by a defibrator is coated with alkali-resol-type phenol resin (concentration of 50%) by a spray so that the phenol resin comes to 8% in terms of resin solid content to 100 pares of fully dried weight of the fiber and thereafter set in a wood frame with a side length of 30 cm to preliminarily mold it. The workpiece is hot-pressed by a hot press same as that of the embodiment 1 except to use a quadrangular-frame-like spacer with a thickness of 30 mm and having steam injection holes.

That is, a preliminarily-molded fiber mat is mounted on a bottom heating plate kept at a temperature of 180 0 C, the bottom heating plate is raised, and the fiber mat is hotpressed for 1 min between the bottom heating plate and the top heating plate. similarly kept at a temperature of 180 0 C by applying a pressure of 20 kg/cm 2 After one minute passes, the pressure is lowered to 10 kg/cm 2 to continue the hotpressing. When the pressure of the press exceeds 10 kg/cm 2 the steam with a temperature of 180 0 C and a pressure of kg/cm 2 is injected from the injection holes of the spacer for 1 min. After one minute passes, the pressure of the space enclosed by the spacer is returned to the normal pressure and compression is further continued for 1 min. Thereafter, tho workpiece is taken out of the hot press and left as it is for 17 approx. one week at the room temperature to obtain a fiber mat with a thickness of 30 mm.

<Comparative example 2> A hot press is used which is the same as the embodiment 1 except to set two square-pole-shaped spacers with a thickness of 30 mm free from injection holes to a top heating plate along the both sides of a workpiece. Top and bottom heating plates are kept at 180 0 C respectively to hot-press a fiber mat same as the embodiment 2 at a pressure of 20 kg/cm 2 for the first 3 min and thereafter hot-press it at a pressure of kg/cm 2 for 10 min. Then, a fiber mat with a thickness of mm is obtained similarly to the case of the embodiment 2.

On the fiber mats of the embodiment 2 and the comparative example 2 thus obtained, the bending strength, peeling strength, and thickness increase rate are measured in accordance with the P-type test method specified in JIS A 5906. Table 2 shows the test results.

[Table 2]

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o:

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Specific Bending Peeling Thickness gravity strength strength increase rate Embodiment 2 0.70 216 kgf/cm 2 5.8 kgf/cm 2 7 Comparative 0.73 224 kgf/cm 2 4.2 kgf/cm 2 11 example 2 The fiber mat of the embodiment 2 also shows the same physical property values as those of the embodiment 1 and the comparative example 1 compared to the fiber mat of the comparative example 2.

18 <Embodiment 3> The kaoliang stalk 20 having the epidermis 20a mainly made of lignocellulose and the porous medulla 20b at its core shown in Fig. 5 is directly compressed by the compression rollers 21 and 22 without cutting open the stalk 20 to cause a crack 23 in the epidermis 20 as shown in Fig. 6. The kaoliang stalk 20 is soaked in a phenol resin solution to impregnate the stalk with phenol resin up to 15 wt%. Then, though not illustrated, a lot of compressed kaoliang stalks are formed into a sheetlike object by netting them like a reed screen with a string and then five sheet-like objects 30 are superimposed so that component stalks intersect each other while applying an adhesive to them at a rate of 250 g/cm 2 for each bcdi.:layer.

The top and bottom heating plates 11 and 12 of the hot press 40 shown in Fig, 4 are kept at a temperature of 150 0

C

and then the five sheet-like objects 30 are compressed by the heating plaEYs 11 and 12. The top heating plate 11 is S provided with the quadrangular-frame-shaped spacer 14 with a thickness of 30 mm having steam injection holes 14b. When the pressure reaches'8 kg/cm 2 the steam with a temperature of 150°C and a pressure of 5 kg/cm 2 is injected for 5 min. After the steam is injected, the space enclosed by the spacer 14 is decompressed by a decompression pump. After hot-pressing the sheet-like objects for a total of 10 min, a laminate of the sheet-like objects is taken out and left as it is for approx.

one week at the room temperature.

19 <Comparative example 3> As shown in Fig. 11, a laminate of sheet-like objects same as the embodiment 3 is hot-pressed under the same condition as that of the embodiment 3 by using a hot press in which the steam injection hole 2a (which is not illustrated for the heating plate 1) are formed on the pressing surfaces of the top heating plate 1 and the bottom heating plate 2 and a spacer is not attached thereto. Because no spacer is used, steam is not injected from injection holes.

As the result of comparing the laminate of the embodiment 3 with that of the comparative example 3 both of which are thus obtained, irregularity occurs on the surface of the laminate of the comparative example 3 and a problem occurs in the surface smoothness. However, the laminate of the i embo.liment 3 using a spacer has a smooth surface and there is no problem.

In the case of the above embodiments, though a spacer is secured by screws, it is possible to use a means such as welding or bonding.

Moreover, in the case of the above embodiments, a spacer S is set to a bottom or top heating plate, However, it is also possible to set a spacer to both top and bottom heating plates respectively.

Furthermore, the shape of a spacer is not restricted to a quadrangular frame. When the shape of a workpiece is polygonal, it is possible to form a spacer into an enclosing body corresponding to the shape.

20 Furthermore, though a top heating plate lowers or a bottom heating plate rises to press a workpiece in the case of the above embodiments, it is also possible that both heating plates is made movable to press a workpiece.

Furthermore, though a case of heating with steam is described in the above embodiments, it is also possible to use heated and pressured gas.

As described above, the hot press of the present invention, compared to an existing hot press, allows heated and pressured steam or gas to permeate a workpiece from its lateral to its inside because a spacer is provided with injection holes, and thereby makes it possible greatly decrease the hot-pressing time and thus remarkably improve the productivity.

Moreover, when securing a spacer with screws, a flexible and inexpensive hot press can be realized by replacing only spacers in-accordance with the size of a workpiece, Furthermore, it is possible to produce steam by setting only a spacer to a heating plate for pressing of an existing hot press and therefore the existing hot press can effectively be used.

Furthermore, it is possible to inject steam or gas into a workpiece even if materials inferior in the water resistance or sheet-like objects inferior in the air permeability are superimposed on the top and bottom surfaces of the workpiece, and moreover keep the surface of a product smooth and 21 therefore prevent stains from attaching to the surface of the product, compared to an existing hot press oK injecting steam or gas from a heating plate.

Furthermore, compared to an existing hot press, not only the hot-pressing time is decreased by 10 to 90% but also there are advantages that thickness unevenness and thickness increase rate are decreased and mechanical strength is improved.

a, 22

Claims

1. A hot press including a top heating plate, a bottom heating plate, and a specer set to either or both of the pressing surfaces of the top heating plate and the bottom heating plate to determine a machining thickness of a workpiece to be pressed by the both heating plates; wherein the inner surface of the spacer facing the pressed workpiece are provided with a plurality of injection holes for injecting pressured and heated steam or gas.

2. The hot press according to claim 1, wherein the spacer has a thickness of at least 15 mm.

3. The hot press according to claim 1 or claim 2, wherein the spacer serves as an enclosing body for enclosing the workpiece correspondingly to a shape of the workpiece and is removable from the hot press and constituted so as to hermetically seal the workpiece together with the top heating plate and the bottom heating plate under a pressured state.

4. The hot press according to any one of the preceding claims, wherein the workpiece is a laminate made by superimposing one or more objects selected from the group consisting of a sheet of plywood, a sheet of laminated veneer lumber, a particle board, a flake board, a fiber board, a hard board, and a sheet-like object which i made of lignocellulose.

5. The hot press according to claim 4, wherein 4 sheet-like object made of lignocellulose is a sheet-like molded object made of a plurality of plant stalks of bagasse, cotton, bamboo, sunflower, koaliang, corn, sorghum, or sugar cane.

6. A hot press substantially as hereinbefore described with respect to any one of the embodiments illustrated in the accompanying drawings. DATED: 28th April, 1995 PHILLIPS ORMONDE FITZPATRICK Attorneys for: KOYO SANGYO CO., LTD. -23- ABSTRACT A hot press 1iC comprises a top heating 11, a bottom heating plate 12, and a spacer 14. It is preferable that the spacer is removably set to either or both of the heating plates in order to determine the machining thickness of a workpiece 13 to be pressed by both heating plates. A plurality of injection holes 14b for injecting pressured and heated steam or the like are formed on the inner surface 14a of the spacer facing the pressed workpiece. It is preferable that the spacer serves as an enclosing body for enclosing the workpiece and hermetically seals the workpiece together with the heating plates under a pressured state. Even workpieces with different sizes are efficiently and inexpensively pressed and the mechanical strength of a product is improved by effectively using a heating plate for pressing of an existing hot press. It is possible to make steam or the like permeate a workpiece even if plate-like objects inferior Sin the air permeability or materials inferior in the water resistance are superimposed on the surface of a workpiece and moroever keep the surface of a product smooth and prevent stains from attaching to the product surface. 1 3C ABSTRACT A hot press 10 comprises a top heating 11, a bottom heating plate 12, and a spacer 14. It is preferable that the spacer is removably set to either or both of the heating plates in order to determine the machining thickness of a workpiece 13 to be pressed by both heating plates. A plurality of injection holes 14b for injecting pressured and heated steam or the like are formed on the inner surface 14a of the spacer facing the pressed workpiece. It is preferable that the spacer serves as an enclosing body for enclosing the workpiece and hermetically seals the workpiece together with the heating plates under a pressured state. Even workpieces with different sizes are efficiently and inexpensively pressed and the mechanical strength of a product is improved by effectively using a heating plate for pressing of an existing hot press. It is possible to make steam or the like permeate a workpiece even if plate-like objects inferior in the air permeability or materials inferior in the water resistance are superimposed on the surface of a workpiece and 2Q moroever keep the surface of a product smooth and prevent stains from attaching to the product surface.